It is well known that various hydrocarbon aryl halides (Ar-X) may be converted to hydrocarbons such as Ar-H and Ar-Ar in the presence of zerovalent nickel catalysts, comprising nickel solubilized by coordinated ligands, e.g. triphenylphosphine ligands. The aryl halide and the nickel triphenylphosphine react to form an oxidative addition product which may be decomposed by heat to yield said hydrocarbons. The oxidative addition products have also been electrochemically decomposed to said hydrocarbons. For example see, Schiavon et al, J. Chem. Soc. Dalton, 1074 (1981); Siebelle et al, J. Chem. Research (M), 2201 (1980); Bontempelli et al, Inorg. Chim. Acta, 42, 211 (1980); Troupel et al, J. Chem. Res. (S), 26 (1980); Sibelle et al, J. Chem. Res. (S), 268 (1980); and Troupel et al, J. Organomet Chem., 202, 435 (1980).
Hughes, J. Org. Chem., 36, 4073 (1971) and Troupel et al, J. Chem. Res. (M), 173 (1980) teach methods for preparing soluble nickel complexes. In both references it is suggested that said soluble nickel complexes form an oxidative addition product with aryl halides, but said product is not decomposed to further products by either author.
Cassar et al, Advances in Chemistry Series, 132, 252 (1974) and Cassar et al, J. Organomet Chem., 173, 335 (1979) report that cyanide ion not only promotes deactivation of nickel catalyst complexes but also inhibits the reduction of nickel II complexes similar to those investigated in the above Bontempelli references to the catalytically active nickel complexes.
The authors of the above Bontempelli papers have noted in Bontempelli et al, J. Chem. Soc. Dalton Trans., 1887 (1977); Bontempelli et al, Anal. Chem. 49, 1005 (1977); and Seeber et al, J. Electroanal. Chem., 92, 215 (1978) that various nickel II complexes having phosphino and cyano ligands may be electrochemically reduced to active soluble nickel catalyst complexes only at very low temperatures. For example, nickel II phenylphosphine cyanide complexes when electrochemically reduced at temperatures above 0.degree. C. appear to form nickel metal and free phosphine rather than a soluble Ni.degree. complex.
Various patentees teach processes for regenerating catalysts which have become deactivated in use. For example, in U.S. Pat. No. 1,185,500 mercury catalysts are regenerated in a two-step process which reduces various mercury salts to metallic mercury which is subsequently reoxidized to yield catalytically active mercuric salts. Also, U.S. Pat. No. 3,067,276 teaches a three step process for regenerating electrode catalysts. In the third step, regeneration is effected by indirect reduction of the various metal salts comprising said electrode catalysts by using electrolytically produced hydrogen. The electrode catalysts disclosed in this reference are heterogeneous catalysts rather than homogeneous (soluble) catalysts.
In U.S. Pat. No. 3,477,018 a catalyst is non-continuously regenerated by hydrogenation by intermittent contacting of an inactive catalyst with hydrogen. This regeneration process is non-electrolytic, but relies on an electromagnetic method for assessing the activity of a paramagnetic metallic catalyst. Again, the catalyst is a heterogeneous catalyst.
In U.S. Pat. No. 1,431,301 a mercuric salt catalyst is electrolytically regenerated by continuous passage of an oxidizing current. The teaching of this reference is limited to the regeneration of mercuric catalysts. Moreover, the catalyst-reactant system disclosed therein, is a two-phase system, i.e. a heterogeneous catalyst system.
U.S. Pat. Nos. 4,313,803 and 4,313,806 teach a process for electrochemically maintaining the activity of heterogeneous catalysts. In the U.S. Pat. No. 4,813,803 patent, the ratio of metallic copper and a Cu(I) species is adjusted to provide optimum catalytic activity for the conversion of nitriles to amides. The U.S. No. 4,313,806 teaches that the deactivation of Group VIII noble metal catalysts, e.g. palladium metal catalysts, by loss of the Group VIII noble metal, e.g. palladium metal, may be delayed by making the catalyst cathodic with respect to an anode placed in the reaction mixture.